First satellites: Galileo In Orbit Validation Element / GIOVE

Two experimental Galileo satellites - GIOVE-A,GIOVE-B and GIOVE-A2 are part of the first step in the in-orbit validation of the Galileo system. GIOVE-A was orbited by a Soyuz launcher from the Baikonur cosmodrome on 28 December 2005.

GIOVE-B was launched on 27 April 2008 from Baikonour. The launch of the test satellites for Galileo represented some major programmatic achievements:

the first time Europe has flown a navigation satellite

the first time Galileo signals have been transmitted from Space

the first time Europe has flown a satellite in Medium Earth Orbit (MEO)

Europe is meeting the requirements for the Galileo frequency filing

the hydrogen maser clock will be the most accurate clock ever flown in space

GIOVE-A

GIOVE-A structural model

GIOVE-A was developed by Surrey Satellite Technology Ltd (UK). This first mission for a Galileo satellite is a complete success, with the achievement of all its objectives:

securing the frequency filings with ITU: frequencies were brought into use on 3 March 2006

validation of key technologies - all performing largely in line with expectations for the different elements such as the new rubidium clocks

facilitating the experimental reception of navigation signals from Medium Earth Orbit (MEO) - using two transmission channels in parallel

characterisation of the MEO environment using two different radiation monitoring instruments

This 3-axis stabilized satellite has a cubical body of 1.3 m x 1.8 m x 1.65 m with a lift-off mass of 600 kg and a power demand of 700 W provided by two wings of sun-tracking solar arrays each 1.74 m long. The satellite uses a butane propulsion system with two tanks containing 25 kg each.

The satellite carries a payload that transmits a Galileo experimental signal in two separate frequency channels. The main elements of the payload are:

the antenna: a phased array of individual L-band elements, illuminating all the visible Earth below the satellite

the signal generation units: two sets, one able to generate a simple Galileo signal, and another one, able to generate more representative Galileo signals

the clocks: two redundant, small-size Rubidium atomic clocks with a stability of 10 nanoseconds per day

Beyond its expected lifetime of 2 years, GIOVE-A is operating nominally.

GIOVE-B is intended to fulfil similar objectives to GIOVE-A: securing frequency filings, expanding the technologies experimentation to include the passive hydrogen maser clock, characterisation of the MEO orbit using one radiation monitoring instrument, improved signal transmission capabilities using 3 channels in parallel, and enabling expanded signal experimentation.

This is a 3-axis stabilized satellite, with stowed dimensions (with the solar arrays folded) of 0.95 m x 0.95 m x 2.4 m. It will have a lift-off mass of 523 kg and will be equipped with two solar array wings each 1.49 m long supplying up to 700 W of power.

The satellite is using a hydrazine propulsion system with one tank containing 28 kg.

The satellite carries a payload that transmits a Galileo experimental signal on three separate frequency channels. The main elements of the payload are:

the antenna: a phased array of individual L-band elements, illuminating all the visible Earth below the satellite

a navigation signal generation unit with significant flexibility to generate different types of signals

the clocks: one small size rubidium atomic clock with a stability of 10 nanoseconds per day, and a larger passive hydrogen maser clock, another type of atomic clock with better stability (1 nanosecond per day) and which will be the most stable clock ever flown in space

GIOVE-B has reached its expected lifetime of 2 years and is operating nominally. Its operations have been extended.